An objective of crop trait functional genomics is to identify crop trait genes of interest, for example, genes capable of conferring useful agronomic traits in crop plants. Such agronomic traits include, but are not limited to, enhanced yield, whether in quantity or quality; enhanced nutrient acquisition and metabolic efficiency; enhanced or altered nutrient composition of plant tissues used for food, feed, fiber, or processing; enhanced utility for agricultural or industrial processing; enhanced resistance to plant diseases; enhanced tolerance of adverse environmental conditions including, but not limited to, drought, excessive cold, excessive heat, or excessive soil salinity or extreme acidity or alkalinity; and alterations in plant architecture or development, including changes in developmental timing. The deployment of such identified trait genes by either transgenic or non-transgenic approaches can materially improve crop plants for the benefit of agriculture.
Cereals are the most important crop plants on the planet in terms of both human and animal consumption. Genomic synteny (conservation of gene order within large chromosomal segments) is observed in rice, maize, wheat, barley, rye, oats, and other agriculturally important monocots including sorghum (see e.g., Kellogg, 1998; Song et al., 2001, and references therein), which facilitates the mapping and isolation of orthologous genes from diverse cereal species based on the sequence of a single cereal gene. Rice has the smallest (about 420 Mb) genome among the cereal grains, and has recently been a major focus of public and private genomic and EST sequencing efforts. See Goff et al., 2002.
The identification of genes that are important for crop development is an ongoing effort in the agricultural community. Additional information can also be derived from the analysis of the genomes of various important plants. For example, the identification of regulatory elements that control the expression of genes can also lead to the ability to manipulate the plant genome to express polypeptides of interest in specific tissues. In particular, certain plants are becoming the organisms of choice for large-scale production of commercially important proteins such as enzymes. This strategy takes advantage of the fact that during seed development, endosperm cells synthesize large amounts of storage proteins of the zein family, which are deposited in structures known as protein bodies derived from the endoplasmic reticulum. These protein bodies cofractionate with the gluten fraction produced in corn wet milling. The potential therefore exists to generate large quantities of recombinant enzymes in a form associated with gluten or in a more pure form following release of the recombinant enzyme activity from the gluten-associated or immobilized state.
What are needed, then, are new methods and reagents for expressing heterologous nucleotide sequences in plant cells. To meet these needs, the presently disclosed subject matter provides in some embodiments a promoter sequence for directing expression of heterologous nucleotide sequences in plant cells. Also provided are methods for expressing heterologous nucleotide sequences in plant cells using the disclosed promoter.
The presently disclosed subject matter addresses these problems associated with the expression of nucleotide sequences in transgenic plants, as well as other problems.